A NOS 192/24 DAC with the PCM1794 (and WaveIO USB input)

Here are Vdc readings that I just took (4 boards). Also to clarify since this is being used in single ended mode, I have only connected the pos and common (nothing connected to the neg terminals).

Right Channel:
Pos-Com:2.738 mV
Neg-Com:2.714 mV
Pos-Neg: 8.3 mV

Left Channel:
Pos-Com: 2.67 mV
Neg-Com:2.691 mV
Pos-Neg: 0.1 mV
 
Here are Vdc readings that I just took (4 boards). Also to clarify since this is being used in single ended mode, I have only connected the pos and common (nothing connected to the neg terminals).

Right Channel:
Pos-Com:2.738 mV
Neg-Com:2.714 mV
Pos-Neg: 8.3 mV

Left Channel:
Pos-Com: 2.67 mV
Neg-Com:2.691 mV
Pos-Neg: 0.1 mV

This is all perfectly fine and within specs Kartick....

I assumed mV in the versus Common reading is actually Volt?
 
the right channel seemed a tad louder than the left and the image was shifting towards the right on almost all recordings.

Simple monkey test to check where the problem is: reverse the left/right cable connections between DDDAC and (pre)amp. If the left/right problem changes to the other side, look inside your DDDAC. Otherwise, look downstream of the DDDAC.
 
This is all perfectly fine and within specs Kartick....

I assumed mV in the versus Common reading is actually Volt?

My bad, indeed the readings between Pos/Com and Neg/Com are in V and not mV.

Just one more clarification DD, in the other post where I mentioned the left and right channel readings, you did mention that this difference could cause a perceivable channel imbalance and now with the fresh readings, you say all is perfectly within range. Am I not getting something right?
 
Simple monkey test to check where the problem is: reverse the left/right cable connections between DDDAC and (pre)amp. If the left/right problem changes to the other side, look inside your DDDAC. Otherwise, look downstream of the DDDAC.

Did that. With so much of troubleshooting through these years, these monkey tests are the first things I do. With a stereo recording, I could not make it out very clearly. I will however repeat this by playing a mono recording.

Another DIYer friend of mine suggested that if the capacitance values of the output caps are different to one another, that difference could also be the cause of the output imbalance that I am hearing. I measured the capacitance values of the 0.47uf Russian K40Y-9 PIO rated caps and the readings are as follows:

Cap1: .472uf
Cap2: .454uf

Can this be the cause of the channel imbalance?
 
Simple monkey test to check where the problem is: reverse the left/right cable connections between DDDAC and (pre)amp. If the left/right problem changes to the other side, look inside your DDDAC. Otherwise, look downstream of the DDDAC.

well, first you mentioned different readings, so it might had been...

now that you give new values in single end, that shows all is fine.

Just swap the transformers and see if the problem stays or not....

To clarify, both sets of readings (yesterday's and today's) were taken in single ended config, i.e., with output capacitors.

If you notice, the readings between Pos and Common on both channels are pretty close between the first reading i posted yesterday and what i measured today.

First reading:
Right channel output (between POS and COMMON): 2.75 Volts
Left channel output (between POS and COMMON): 2.67 Volts

Today's reading:
Right Channel:
Pos-Com:2.738 mV
Neg-Com:2.714 mV
Pos-Neg: 8.3 mV

Left Channel:
Pos-Com: 2.67 mV
Neg-Com:2.691 mV
Pos-Neg: 0.1 mV
 
First reading:
Right channel output (between POS and COMMON): 2.75 Volts
Left channel output (between POS and COMMON): 2.67 Volts

kartick, we already discussed this a few times in the past. The DC bias values you reported are just that: DC. You cannot hear DC. What you hear is from the AC signals, which are independent of the DC bias point (as long as the DC bias is within the normal operating range). Slightly different DC bias between left and right channels are therefore entirely irrelevant.

What is relevant is that the POS / NEG DC bias voltages within a given channel are balanced in order to avoid saturation of the transformers.

Just read up Doedes DDDAC website and the many posts about this to remember what this all about.

Apart from this, I would not be surprised if your NOS capacitors are a bit beyond their "expiry date". Just use some modern no-nonsense capacitors that will be transparent to the audio signal.
 
It's a little strange that the measurements don't match well.

Right channel: 2.738V-2.714V=+0.024V (+24mV). Directly measured POS-NEG: +8.3mV It should be the same (+24mV) and it is not.

Left channel: 2.67V-2.691V= -0.021V (-21mV). Directly measured POS-NEG: +0.1mV

I have absolutely no idea as to why this is happening and even how to rectify this, if there is anything to be rectified in the first place. I remember I posted this earlier as well and my readings were this (post #6919), quite similar.
 
kartick, we already discussed this a few times in the past. The DC bias values you reported are just that: DC. You cannot hear DC. What you hear is from the AC signals, which are independent of the DC bias point (as long as the DC bias is within the normal operating range). Slightly different DC bias between left and right channels are therefore entirely irrelevant.

What is relevant is that the POS / NEG DC bias voltages within a given channel are balanced in order to avoid saturation of the transformers.

Just read up Doedes DDDAC website and the many posts about this to remember what this all about.

Apart from this, I would not be surprised if your NOS capacitors are a bit beyond their "expiry date". Just use some modern no-nonsense capacitors that will be transparent to the audio signal.

Sure, I am already looking for some good capacitors. I recently procured Miflex caps from Poland but I have 0.47uf values. When I shifted from the Russian 0.47uf PIOs to a local brand with 2.2uf capacitance, I heard a smoother, fuller and sweeter sound. It is making think of going to 2.2 or higher cap value. I might even go balanced by putting 2 caps across each channel, as some other folks here have done. I certainly need that extra voltage out.
 
I played around with the output resistors a bit, rearranged them and replaced some, and got approximately 2-3mV DC offset on both channels. In general, it was not much needed, but when I am already experimenting with the output transformers, I want it to be as close as possible to the ideal (0 mV DC offset).

Let's say on the ISKRA transformer, the primary resistance is 20 ohms, the DC offset of 2mV gives a DC current of 0.1mA, completely negligible. Even with ten times the offset, it is 1mA, which is also negligible.

For output capacitors, depending on the money you want to spend I suggest:
Mundorf EVO Aluminum Oil 4.7uF 450VDC from the cheaper ones, or
Jantzen Silver Z (or Superior Z) from the more expensive, also 4.7uF but 800VDC.


Of course there are better and worse options, I have tried these In DAC, tube preamp, speakers ... and I say, they are very good/excellent.
Jantzen has a brighter sound, but EVO Oil has a nicer midrange, but it's not as transparent. How it will really sounds, depends a lot on the rest of the system.

Humble Homemade Hifi - Cap Test
 
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Current status with the new Pi streamer with FIFOPi and battery PSU with super caps :D
 

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kartick, we already discussed this a few times in the past. The DC bias values you reported are just that: DC. You cannot hear DC. What you hear is from the AC signals, which are independent of the DC bias point (as long as the DC bias is within the normal operating range). Slightly different DC bias between left and right channels are therefore entirely irrelevant.

What is relevant is that the POS / NEG DC bias voltages within a given channel are balanced in order to avoid saturation of the transformers.

Just read up Doedes DDDAC website and the many posts about this to remember what this all about.

Apart from this, I would not be surprised if your NOS capacitors are a bit beyond their "expiry date". Just use some modern no-nonsense capacitors that will be transparent to the audio signal.

I played around with the output resistors a bit, rearranged them and replaced some, and got approximately 2-3mV DC offset on both channels. In general, it was not much needed, but when I am already experimenting with the output transformers, I want it to be as close as possible to the ideal (0 mV DC offset).

Let's say on the ISKRA transformer, the primary resistance is 20 ohms, the DC offset of 2mV gives a DC current of 0.1mA, completely negligible. Even with ten times the offset, it is 1mA, which is also negligible.

For output capacitors, depending on the money you want to spend I suggest:
Mundorf EVO Aluminum Oil 4.7uF 450VDC from the cheaper ones, or
Jantzen Silver Z (or Superior Z) from the more expensive, also 4.7uF but 800VDC.


Of course there are better and worse options, I have tried these In DAC, tube preamp, speakers ... and I say, they are very good/excellent.
Jantzen has a brighter sound, but EVO Oil has a nicer midrange, but it's not as transparent. How it will really sounds, depends a lot on the rest of the system.

Humble Homemade Hifi - Cap Test

Thanks Nixie. I have placed an order for 4 4.7uf Obbligato Gold Premium capacitors. Will try to wire the dac in a balanced mode using 2 caps each on each of the channels. Really need the extra voltage out for the headroom with my tube preamp. Will report back my initial observations by this weekend.
 
Kartick, does your tube amp have balanced inputs? Does it have DC blocking caps at the input? Can you share a schematic of the amp input stage?

No, my tube amp does not have balanced inputs. Even when I was using the Cinemags, I was converting the transformer outputs to single ended RCA jacks, which were in turn connected to the single ended RCA inputs of my tube pre.

I shall confirm regarding the DC blocking caps at the input and the schematic of the amp input stage tomorrow post checking with the amp designer.
 
In this case you can't use the balanced out from the DDDAC with cap coupling. You'll need a transformer to convert the DDDAC balanced output to single ended input of your amp.

If your amp was made by a competent builder I'd be surprised if there is no DC blocking cap. In this case you could directly connect the POS + GND from the DDDAC to the RCA input of your amp. No need for coupling caps.

Sorry for spoiling your "fun" with exotic and overpriced caps. If you still want a coupling cap, just get some Panasonic of Wima MKPs from Mouser or Digi Key, etc. However, I believe you would be best off by putting the transformers back in there.
 
In this case you can't use the balanced out from the DDDAC with cap coupling. You'll need a transformer to convert the DDDAC balanced output to single ended input of your amp.

- Is it? I believe Nixie is also using 2 Jantzen Silver caps across each channel and still using it in the single ended mode (check post#8150). Anyway, my question, if I am using a transformer and still going single ended to my preamp, why cant I use the Pos/Neg from the dac board to 2 caps each and yet go single ended to my pre?

If your amp was made by a competent builder I'd be surprised if there is no DC blocking cap. In this case you could directly connect the POS + GND from the DDDAC to the RCA input of your amp. No need for coupling caps.

- As I said, I can confirm for sure tomorrow about the dc blocking caps on the amp's input section. However, here is my argument - It is alright to consider going out without caps from the dac to the preamp as the caps on the inputs will block the DC. But in case my amp doesnt have any dc blocking caps, wont having caps on the DAC's output effectively mean the same thing?

Sorry for spoiling your "fun" with exotic and overpriced caps. If you still want a coupling cap, just get some Panasonic of Wima MKPs from Mouser or Digi Key, etc. However, I believe you would be best off by putting the transformers back in there.

- Actually TBH, I am actually someone who doesn't run after exotic stuff. Proof is that I was still attempting to utilise my good old Russian PIOs. But just since I had these Obbligatos locally available in India, I ordered those. We don't have much choices in India and Digikey/Mouser charge insane shipping and custom duties on the products. I dint spend a fortune on these caps anyway. Regarding transformers, I am not sure if Cinemags gave me the dynamic output I always craved from the DAC (specially in the bass department). They were good but I am not sure if they were as good as the cap coupled output. I will use the new caps and go back to Cinemags to see what those do. Anyway, i think soon it will be time to go to the Sowters. But before that investment, I would like to take away the channel imbalance from the DAC.
 
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I think @mbrennwa, you are right about the caps not being usable in balanced mode if the amp is SE. I see that being discussed in post #8194.

Is there no way of doubling the voltage when using caps? Why cant 2 caps be used on each channel and voltage be doubled as with the case of a trafo?

Would request Nixie62 to clarify if he means we can use 4 caps as he mentioned in post #8444 even we are taking the outputs to a SE input of the preamp?
 
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